COURSE INTRODUCTION

Software Tools EECS2031 Winter 2018 Manos Papagelis

Thanks to Karen Reid and Alan J Rosenthal for material in these slides What EECS2031 is about?

 A useful way to think about this course is that it is about the environment in which your programs run  understanding the environment  developing tools:  for interacting with the environment  for getting information about it  for influencing it  learning a new language (or two) to help us Course Overview

 Part I (UNIX, Shell Programming) ~3 Weeks  UNIX  Understanding the Shell and Shell Programming  Part II (C Programming) ~7 Weeks  C Fundamentals, Input/Output  Expressions, Selection Statements, Loops, Types  Arrays, Functions  Pointers, Arrays, Strings  Structures, Dynamic Memory Management  Part III (UNIX Programming) ~2 Weeks  Processes, Signals, Pipes Self Study Topics

 Using Unix - some tutorial coverage

 Using software tools  an editor – vi, emacs, nedit, …  a debugger – gdb, …  an IDE – eclipse, …

 Readings Environment

 Environment: EECS Computing Facility  UNIX/LINUX system  SSH to eecs.yorku.ca  Use your EECS login and password Windows & Mac Users

 Windows: If you want to do some of your work on your own machine, you will need to install cygwin:

http://www.cygwin.com/

 MacOS: Use the “Terminal” application For my interest

 How many of you have UNIX/LINUX knowledge?

 How many of you have done some shell scripting?

 How many of you have programmed in C or had attended an introductory course in C?

 How many of you have understanding of processes, pipes, signals in UNIX environment? Today’s Overview

 Course Administrivia

 Unix & Unix as a File System

 The Big Picture EECS2031 Administrivia Course Information

 Lectures (CLH E):  Tue, 9:30-10:30am  Thu, 9:30-10:30am  Tutorials/labs (LAS1006):  Lab01: Tue, 13:00-15:00  Lab02: Wed, 13:00-15:00  Course Website (soon online): https://www.eecs.yorku.ca/~papaggel/courses/eecs2031/ Communication

 Office hours:  TR 10:30am – 11:30am  by appointment in special cases  Email:  Subject must include EECS2031  Email is a formal method of communication:  State your question clearly, with enough context  Sign it (Name, login and student # are the most useful) Course Textbooks

• C Programming: A Modern Approach, Second Ed., K.N. King. W. W. Norton and Company, 2008. • (optional) Unix System Programming Second Edition, Keith Haviland, Dina Gray, Ben Salama. Addison-Wesley, 1998. • (optional) The Linux Programming Interface, Michael Kerrisk. No Starch Press, 2010. Assignments

 A1: Shell Use and Programming

 A2: Tools in C (Loops, Arrays, Strings)

 A3: More tools in C (Dynamic Memory Management, Files, Linked Lists)

All assignments, tests and exam are individual work Assignment Policies

 Assignments are due at 11:59 p.m. on the due date - check website for final due dates  Late Assignment Policy: 3 grace days  Code must work on EECS servers  Marking  assignment 1, 2, 3: (mostly) based on auto-markers  Code that does not compile gets zero Did you catch that?

Code that does not compile will receive a grade of 0 Submitting Assignments

 You will be using the submit tool to manage and submit your assignments

 Details will be provided on how to submit your assignments

 Do not wait until the last minute to try to commit your assignment for the first time Plagiarism

 “The work you submit must be your own, done without participation by others. It is an academic offense to hand in anything written by someone else without acknowledgement.”

 You are not helping your friend when you give them a copy of your assignment

 You are hurting your friend when you ask them to give you a copy of their assignment What is Cheating?

 Cheating is  copying parts or all of another student’s assignment  including code from books, web sites, other courses without attribution  getting someone else to do substantial parts of your assignment  giving someone else your solution  Cheating is not  helping to find a bug in a friend’s code (be careful)  helping each other understand man pages or example code A few do’s and don’ts

 Do  ask questions if you don’t understand something  work together to understand concepts/assignments  use tutorials/labs and office hours  read textbook or provided online material before class

 Don’t  hand in other peoples’ work (it’s cheating)  harass others (see the University’s policies)  distract or disrupt the class (it’s immature) Course Marking Scheme

Work Weight Comment

3 Assignments 45% 15% each

Midterm Test 15% In-class, paper-based

You must get >=40% in the Final Exam 40% final exam to pass the course UNIX Unix History

 Developed in 1969 (in assemply) by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, Michael Lesk and Joe Ossanna.  Dennis Ritchie and Ken Thompson ported an enhanced version to a PDP-11/20 in 1970.  Ritchie and Rudd Canaday ported a cut down version of the BCPL language to Unix, calling it B.  Pipes and C (successor of B) were added in 1971-73  “License to universities, but no support.”, BTL Lawyers  This led to extensive sharing More Unix History

 Canadian connection: Brian Kernighan, Rob Pike, Bill Reeves, ...  Berkeley Software Distribution grew out of collecting and distributing bug fixes (Led to FreeBSD, NetBSD)  Bill Joy started at Berkeley but joined the startup Sun Microsystems in 1982  1991, Linus Torvalds (Linux kernel initiator) posts a note describing his experimental OS modeled on Minix (Unix-like OS) Evolution of Unix and Unix-like Systems

Minix Linux MacOSX FreeBSD Android … Why Unix?

 Multi-user, multi-tasking computer operating system  Available on a number of platforms  Shares computer resources sensibly  Permits manipulation of files, processes, and programs  Allows inter-process and inter-machine communication  Permits access to its operating features The Unix Philosophy

 Write programs that do one thing and do it well

 Write programs to work together

 Write programs that handle text streams, because that is a universal interface Ways of Looking at a System

 Some of the ways we look at UNIX:  As an end user  As an environment for programs to run  As a file system - part of the overall environment UNIX: End-user Interaction

 Unix has a rich set of tools for dealing with its own structures and data:  need to be familiar with them to manage (your portion of) the system  you may already know some (i.e., move around filesystem, list, copy and remove files, run programs and performing other tasks)

 Involves learning how to write UNIX shell scripts UNIX: Environment for Programs

 How programs get ready to run

 What happens when a program is run

 What happens when your program writes to/reads from a file

 How your code can start other pieces of code and interact with them  how programs "talk" to each other  how programs "talk" to the outside world (networks) UNIX: As a File System

 What are files? what are directories?  how are they organized, maintained?  what information is accessible about them?

 What different file types are there?

 How to access them? Unix as a File System Files and Directories

 “Everything is a file.”

 Unix provides a file interface for all Input/Output.  regular files Try ls –l /dev and look  directories at the permissions string.  devices crw------brw------ video (block) c = character, b = block  keyboard (character)  sound (audio)  network (block)

 File interface = open, read, write, close File System Hierarchy

 Everything starts in the “root” directory whose name is “/”

 A directory is a file that contains directory entries

 A directory entry maps a file name to an inode

 An inode is the data structure that contains information about a file, including which disk blocks contain the file data File System Hierarchy

/ hard link

u h usr

u1 u2 u3 bin lib

c4 csc209h symbolic reid 01 links winter c4reidka Use df to see all the different disk pub partitions on EECS servers. repo Haviland File Systems and Links Ch. 4.5, 4.3, 3.2

 One file system per disk partition

 A file system can be mounted at any point in the directory tree of another file system

 A hard link is an entry in a directory file which specifies an inode

 There can be several hard links to a file, but hard links cannot cross file systems

 A soft link (symbolic link) is a small file containing the path name of the linked file or directory

 Soft links work across file systems Directories and Links

directory file

2 . 2 .. 14 u 46505 home 139412 cdrom 201345 lib

% ls –l / drwxr-xr-x 2 root root 4096 Nov 8 17:56 bin/ drwxr-xr-x 2 root root 4096 Aug 10 14:46 cdrom/ drwxrwsr-x 2 root staff 4096 Feb 8 2002 home/ drwxr-xr-x 6 root root 4096 Sep 2 15:26 lib/ lrwx------1 root root 6 Sep 2 15:32 u -> /cdf/u/ Inodes and Directory Entries

Inode 12345 Directory Entry size owner UID, GID 12345 afile access time modified time creation time link and block counts permissions

direct pointers to file blocks single indirect pointer pointers to double indirect pointer next file blocks triple indirect pointer Haviland Stat Ch 3.3

stat(): A Unix system call that returns useful data about a file inode

greywolf% stat csc209h File: `csc209h' Size: 512 Blocks: 2 IO Block: 8192 directory Device: 16h/22d Inode: 27612 Links: 7 Access: (0755/drwxr-xr-x) Uid: ( 0/ root) Gid: ( 517/ csc209h) Access: 2010-01-06 11:32:44.293409000 -0500 Modify: 2010-01-04 12:06:15.987312000 -0500 Change: 2010-01-04 12:06:15.987312000 -0500 Permissions Ch 3.1

-rwxr-xr-x 1 reid 0 Jan 6 11:35 allexec* -r--r--r-- 1 reid 0 Jan 6 11:35 allread dr-xr-xr-x 2 reid 512 Jan 6 11:36 dir-read/ dr-x--x--x 2 reid 512 Jan 6 11:36 dir-search/ -rw------1 reid 0 Jan 6 11:35 ownerread -rwxr-xr-x -r--r--r-- 1 reid 0 Jan 6 11:35 readonly

 File permissions  read, write, execute – pretty much what you think  Directory permissions  read: you can “read” the file (run ls, cat, etc.)  write: you can “write” (create/edit/delete) the file  execute: you can “execute” the file  Use chmod to change file permissions  e.g.: % chmod 664 myfile THE BIG PICTURE The Big Picture

Source code file Compile it Object file hw.c hw #include void main() { % gcc –o hw hw.c printf("Hello world"); }

Run it Process

% hw Source Code Files

hw.c  What is a file? #include void  Sequence of bytes main() {  A file system? printf("Hello world"); }  A hierarchy of files + tools  How does the system know where to find hw.c?

 paths, working directories, …

 What is the meaning of #include ?

 What does printf really do? Compiling a program

% gcc –o hw hw.c  A compiler is a program that translates source code into object (machine) code

 Here we are running the compiler at the command line The Shell

% gcc –o hw hw.c  The % is a shell prompt  The shell is a program that can execute another program  The shell  accepts commands (programs) as input  finds the executable  interprets the arguments  starts executing the command  The shell also has some “built-in” commands Running a program

% gcc –o hw hw.c  After we have compiled the program, we can run it

% hw  load a program into memory and hand it off to the OS that takes control of running it A Different Big Picture

sh less vi perl gcc nedit grep ddd

libc – C Interface to Unix system services

Unix system services (system calls)

Unix kernel (in C)

computer Processes

 A process is an executing instance of a program

 The OS keeps track of information about the process  process ID – a unique non-negative integer  process state – “running”, “ready”, “blocked”  program counter – which instruction is being executed  a list of open files  etc. Object Files/Executables

high address  Typical memory layout stack of programs.

 The kernel keeps a Process control block (PCB)

sp (stack pointer) PCB for each process

pc (program counter) ... heap

uninit. data init. data

text low address What is Next?

 Shell & Shell Programming

 Tutorial about UNIX (next week)

 Tutorial about Shell scripting (week after)